The present invention relates to a novel use of peroxidized lipids as agents intended to prevent and/or to treat the irritant effects of an active principle.
More specifically, the invention relates to a composition for topical application to the skin for treating or preventing irritation due to the irritant nature of an active principle comprised in said composition and to a method of treating of human body intended to treat or prevent the irritant effect of an active principle.
It is well known that a certain number of active principles intended to be used topically on the skin, especially active principles used in dermatology, are capable of generating severe or even very severe tolerance problems. The secondary effects of these active principles can range from simple irritation up to manifestations of eczematous type, risks of blisters or vesicles on the skin.
An example of a well-known product causing such effects is capsaicin which corresponds to the formula: 
It is a product which is well known for its vasodilatory action. Owing to this action, capsaicin is widely used in preparations for local use whose effect is to obtain an influx of blood and a sensation of heat. To this end, capsaicin is very particularly indicated in the treatment of pain in rheumatology. However, one of the disadvantages of this product is that it is an irritant product which causes smarting of the skin.
Another example of a product also known for its particularly irritant character is constituted by retinoic acid, alternatively called vitamin A acid, the active principle particularly used in topical compositions intended for the treatment of acne and of wrinkles.
Finally, other active principles are also well known for their irritant character. Mention may be made, in particular, of synthetic retinoids, 5-fluoro-uracil, benzoyl peroxide as well as nicotinamide and salicylic acid.
Various peroxidized lipids, especially obtained by peroxidation of natural vegetable oil, are known. Mention may be made, in particular, of the following patents BSM No. 2 330 M, EP-A-293 535, FR-A-2 591 112, EP-A-225 831, EP-A-225 832, EP-A-225 833, EP-A-226 506, FR-A-2 461 744, FR-A-2 539 142 and EP-A-117 962, which concern either the preparation of such peroxidized lipids or their application in various fields, in particular in the treatment of certain conditions in the field of rheumatology or of traumatology, or alternatively as a cicatrizing product.
European Application EP-A-0 481 148 describes pharmaceutical compositions, and especially pharmaceutical compositions from the tumor therapy field, containing, as active principles, a hyperoxygenated oil and an oxygenated derivative of retinene, in combination with a vehicle or a non-irritant pharmaceutically compatible inert excipient. In these compositions, the hyperoxygenated oil is used at doses of always less than 5% by weight and their aim is to promote the passage of the retinene derivative into the dermis and its attachment to the lesions to be treated.
It has now quite surprisingly been discovered that it was possible to considerably decrease the irritant character of an active principle, especially of a pharmaceutical active principle, in particular of a dermatological active principle, for topical application by simultaneously applying to the skin a sufficiently large quantity of a composition containing a sufficiently large quantity of peroxidized lipids.
Thus, the present invention relates to a novel use of peroxidized lipids, in particular of peroxidized oils, as agents intended to prevent and/or to treat the irritant effects of an active principle.
According to a particularly advantageous aspect, the invention relates to compositions, especially pharmaceutical compositions, containing at one and the same time the irritant active principle and a sufficient quantity of peroxidized lipids.
Thus, for example, according to a first aspect, the invention relates to novel compositions for topical application to the skin, containing an active principle, especially a pharmaceutical active principle, with irritant character in a cosmetically or pharmaceutically acceptable vehicle containing more than 5% by weight of peroxidized lipids.
Given the severe character of irritation phenomena which the present invention proposes to resolve, the compositions aimed at by the present invention are generally compositions from the pharmaceutical field, in particular from the dermatological field.
The peroxidized lipids whose use is claimed according to the present invention result from the peroxidation of unsaturated fatty substances.
The degree of peroxidation is measured according to the standard ISO 3960.
To carry out the present invention, peroxidized lipids having a peroxidation level of between 5 and 600 milliequivalents per kilo, preferably between 30 and 500 milliequivalents per kilo, may advantageously be chosen.
This peroxidation level may more advantageously be between 50 and 300 milliequivalents per kilo, more preferably between 50 and 150 milliequivalents per kilo.
The preferred peroxidized lipids used according to the invention result from the peroxidation of lipids of vegetable origin, preferably of lipids from a natural vegetable oil.
Examples of natural oil chosen according to the invention which may be mentioned are sweet almond oil, hazelnut oil, peanut oil, corn oil, grapeseed oil, sesame oil and safflower oil. It is also possible to use a mixture of these oils.
According to a particularly preferred variant of the invention, peroxidized corn oil and very particularly a corn oil having a level of peroxidation of between 5 and 600 milliequivalents per kilo may be chosen.
The peroxidized lipids used according to the invention are advantageously formed of major constituents, generally representing at least 80% of the triglyceride mass, corresponding to the formula 
in which the radicals R are mainly represented by partially peroxidized C18 unsaturated acids (as a function of the level of peroxidation of said lipid).
The compositions of the invention can be in any form compatible with topical application to the surface of the skin. These compositions may preferably be found in the form of an oil-in-water or water-in-oil type emulsion, a cream, a lotion, a milk or a gel, in particular an oily gel based on colloidal silica.
The compositions of the invention contain, for the effect of the peroxidized lipid to be perceptible and to allow the irritant effect of the active principle to be prevented or treated effectively, more than 5% by weight of this peroxidized lipid.
According to an advantageous variant of the invention, the concentration of peroxidized lipids in the composition is between 5 (excluded value) and 97% by weight, preferably between 10 and 95%.
The peroxidized lipids concentration of the compositions of the invention depends, at the same time, on the nature of the active principle with irritant character and on its degree of aggressiveness with respect to the skin. It thus depends at the same time on the concentration and the nature of the active principle. However, it is clear that for the same active principle, this concentration will be all the higher because the concentration of the active principle in the composition will itself be higher.
In addition, and this forms an additional advantage of the composition according to the invention, the presence in the said composition of peroxidized lipids in sufficient quantity allows, if necessary, the customary concentrations of active principle to be perceptibly increased, without having additional risks of irritation.
As set out above, the invention is especially directed at the irritant active principles of compositions known in the pharmaceutical field, especially in the dermatological field.
By way of particularly irritant active principle for which the present invention provides a particularly effective solution, mention may be made of capsaicin, synthetic retinoids, retinoic acid, benzoyl peroxide, nicotinamide, salicylic acid, hydroquinone and 5-fluorouracil.
As is evident in particular from the examples which follow, the invention turns out to be very particularly effective in the case of capsaicin.
According to a particularly advantageous variant of the invention, in the case of capsaicin the composition is in the form of an emulsion of water-in-oil or oil-in-water type containing more than 5 and at the most 50% by weight of peroxidized oil and from 0.010% to 0.080% of pure capsaicin.
According to another variant of the invention and, still in the case of capsaicin, the compositions of the invention may be in the form of an oily gel, especially of a gel based on colloidal silica, and in this case advantageously contain from 40 to 97% by weight of peroxidized oil and from 0.010% to 0.08% of pure capsaicin.
Another active principle for which the invention provides a particularly advantageous solution for avoiding its skin-irritant character is retinoic acid.
In the case of retinoic acid, the composition is advantageously in the form of an emulsion containing, by weight, preferably from 0.010% to 0.07% of pure retinoic acid. The concentration of peroxidized oil of these compositions is greater than 5% by weight and, preferably, between 7% and 90%, preferably between 10 and 50%.
Still in the case of retinoic acid, it is also possible for the compositions to be in gel form, in particular in the form of gels containing from 0.010% to 0.07% by weight of pure retinoic acid per 40 to 97% of peroxidized oil.
Of course, it is additionally possible for the compositions of the invention to comprise different additives conventionally used in this type of composition for topical use, in particular in dermatology.
Thus, for example, it is possible for the compositions of the invention to additionally contain emulsifying agents, perfumes and preservatives of the type conventionally used in compositions for topical use in dermatology.
As set out above, the invention provides a particularly effective means of preventing or treating all the intolerance phenomena connected with the use of pharmaceutical, especially dermatological, products, known for their irritant or very irritant characteristics, the peroxidizing oils acting with an anti-erythematous or anti-reactive action, especially allowing any eczematous reaction as well as any risk of formation of blisters or of vesicles on the surface of the skin to be avoided during the application of an active principle known for its particularly irritant character.
The invention thus offers a means of effectively combating such reactions by applying to the skin, simultaneously, peroxidized oil in sufficient quantity and the active principle, with a view to avoiding the unpleasant symptoms connected with the aggressiveness of this active principle.
The invention thus covers any of the procedures for topical treatment of the skin in which an active principle whose irritant character is known and a sufficient quantity of peroxidized oil are applied simultaneously to avoid all the unpleasant symptoms connected with the application of this active principle to the skin.
Thus, according to a second aspect, the invention relates to a method of preventing irritation due to an active principle applied to a part of the human body, comprising the application to the same part of the body of an effective amount of peroxidized lipids.
According to a first embodiment of the above method, the active principle and the peroxidized lipids are included in the same composition which is a composition as defined above.
According to another embodiment of the invention, the active principle and the composition comprising the peroxidized lipids may be applied separately.
In both cases, the method allows eczematous manifestations, formations of blisters or of vesicles as well as any erythematous action connected with the topical application to the skin of said active principle to be prevented and/or avoided.
As set out above, it is possible to obtain this effect by applying to the skin a composition such as defined above containing the peroxidized oil and the active principle for which it is wished to prevent the irritant effect.
It is also possible to obtain this effect by applying to the skin, conjointly with a composition containing an irritant active principle, a composition containing more than 5% by weight of peroxidized lipids such as defined above.
The compositions which can be used for carrying out this treatment procedure, containing or not containing the active principle for which it is wished to avoid the secondary effects, can be in one of the forms defined above, in particular in gel or emulsion form and can contain different additives conventionally used in the field of dermatology.